The uplink in a cellular radio access network of an E-UTRA is a combination of single-carrier TDMA and Frequency Division Multiple Access (FDMA) with dynamic scheduling, which allows for an orthogonal uplink transmission, thereby avoiding all intra-cell interference. However, transmissions between cells are non-orthogonal as a consequence of single frequency reuse. Thus, the traffic in each cell will contribute to an interference that impacts its neighbouring cells.
Scheduling of user equipments in a cell (i.e. inform user equipments (UEs) when and on what part of bandwidth they are allowed to transmit) and admission of new user equipments to a cell are two of the most basic tasks to be performed in a cell.
Scheduling in E-UTRAN: Scheduling of time and frequency resources among user equipments for uplink communication is complicated by the fact that the scheduler, which is located in the base station, is not automatically aware of the resource demand of the users. This includes, e.g., the type and amount of data that a user intends to transmit but also depends on which users intend to transmit data. The concept for uplink scheduling is based on a resource reservation principle where the user equipment requests permission to transmit data. The UL scheduler monitors the requests of the user equipments and distributes the available resources among the various data flows. Further, the scheduler informs user equipments of the scheduling decision by issuing a resource assignment (or grant) for the transmission. Thus, uplink transmission is scheduled by a scheduling mechanism in the radio base station (i.e. the eNodeB in E-UTRAN) whereby scheduling grants inform the user equipments (UEs) when and at what part of the bandwidth they are allowed to transmit. FIG. 1 illustrates the concept of uplink scheduling.
Scheduling grants are transmitted to the user equipments using the downlink shared control channel. A scheduling grant includes information on the user ID and the resources that are to be used for uplink data transmission (e.g. location in frequency domain, (recommended) modulation scheme, antenna configuration, etc.) The grant may address a specific radio bearer (or logical channel) rather than only a specific UE. This enables the scheduler to enforce priorities between flows from single user equipments. In its simplest form the scheduling grant is valid only for the next UL TTI. However, in order to reduce the amount of required control signalling, persistent scheduling (i.e. the network signals a “scheduling pattern” to the user equipment) may be considered.
Admission control in E-UTRAN: Decisions to admit new users to a cell must consider the interference impact of such a new user on neighbouring cells (as already explained above) and within the own cell as well as the impact from said neighbouring cells. It is preferable to allocate new traffic to frequencies with low interference from neighbour cells. This ensures that the interference level for the new traffic will be low, at the same time as only a small amount of traffic in neighbour cells is likely to be negatively affected by the interference generated by the new scheduled traffic.
On top of eNodeB scheduling, the admission of users needs to be supervised and controlled at a higher level. This is done by the admission control function.
When a user equipment transmits on a subset of tones in the uplink of an E-UTRAN, the corresponding tones of the uplinks of neighbour cells are affected by a corresponding interference. It is hence less beneficial to schedule traffic in neighbour cells to these tones. Furthermore, in case the interference level increases above acceptable thresholds for certain sets of tones in terms of bandwidth, the admission control function preferably does not allow any further user equipments to use these tones.
As a consequence, neighbour cell interference is preferably accounted for when the admission decisions are taken. In order to determine the neighbour cell interference in a specific frequency band, the thermal noise power and the own cell power in said frequency band needs to be measured or estimated, and subtracted from the measured total signal power in said frequency band.
Noting that the interference from cells affects all surrounding cells, the impact of one specific cell on another specific neighbour cell cannot be obtained by only estimating the total perceived neighbour cell interference level. It is thus not possible to perform optimal scheduling and admission control decisions accounting for inter-cell effects.
International patent applications WO 2007/024166 and WO 2008/004924 disclose soft estimation of neighbour cell interference exploiting techniques for soft noise floor estimation applicable for UTRAN. Given the availability of algorithms for estimation of the conditional probability distribution of the thermal noise power floor for the complete uplink frequency band, said documents disclose soft estimation of the discretized conditional probability distribution of the thermal noise power floor of individual tones of the uplink. Further, given measurements of the total uplink power and the own cell uplink power of the tones, said documents disclose algorithms and means for estimation of the discretized conditional probability distribution of the neighbour cell interference, for each tone or subset of tones. The optimal estimate of the neighbour cell interference, as perceived in the cell, together with the corresponding optimal estimate of the variance, may then be computed as conditional means as described in prior art.
Prior art thus discloses means that estimate the perceived neighbour cell interference from other close cells.